DE3930658C2 - - Google Patents

Description

The invention relates to a semiconductor photodetector according to the preamble of claim 1 and a matrix arrangement such photodetectors according to claim 9.

Previously known detector devices, e.g. B. to measure of intensity profiles of a light beam, have large areas Semiconductor structures in connection with fixed or movable columns and apertures. So used at for example the model 1180-HR "Beam Scan" from Photon Inc. installed a stationary large-area photodetector a slit or point aperture circular rotates. In this known, working in real time di rect measurement methods can light beams with a diam measured at least 5 µm at sampling frequencies of 5 Hz will.

Another example of a high-resolution detector is the "Optical Profiler" from Oriel. With this be Known device is a silicon semiconductor structure behind a narrow aperture diaphragm. A motori The detector head moves the aperture diaphragm with the Silicon semiconductor structure along one to be measured Axis. The achievable with this known device solubility is approx. 0.1 µm.

Other known higher resolution detectors for measurement of intensity profiles of light beams work with so mentioned indirect measuring method. The model 0390 "spot Scan "from Photon Inc. calculated using a micro computers the intensity profile of a focused light beam by means of signals covered by a wedge-like th photodetector. With the help of computerized Interpolation techniques are so resolving power of  reached a few nm, the diameter of the measured Spots can range from 0.4 to 10 µm.

The devices known from the prior art for direct measurements are based on their spatial resolution limited to structures over 1 micron, because ge suitable aperture diaphragms with the required manufacturing standards bags in the submicrometer range are not available. The be working in the direct process are therefore suitable knew devices only for capturing beam profiles with a relatively large beam diameter and in the area in which a high resolution is not required is.

The detection of sharply focused intensity profiles with a high resolution is currently only with indirect Measuring method possible. These known methods have the Disadvantage that they are operated only with great effort may require an additional microcomputer and the Involve danger that z. B. in the measurement of im transversal multimode operation lasers fail occur due to unfavorably chosen differentiation methods can.

DE-OS 33 45 214 are pn junctions with intermediate layers known to reduce the noise of the diodes.

From "Avalanche mesa photodiodes with transverse radiation"; O. Krumpholz et. al .; Wiss. Ber. AEG-Telefunken; 44; (1971); 2, it is known from the side of semiconductor layer systems to illuminate to provide a detector that light at wavelengths near the intrinsic absorption edge of the semiconductor material used to detect sensitive be able to. These known detectors own not, however, in order to be high-resolution, in the submicron range working detectors to be used  since the dopants implanted in the semiconductor material used are chosen so that there is a pn transition with a Thickness of a few to 100 microns in the local area. Though could be due to a higher doping of the pn junction Thickness in the local area can be reduced, however this is the case with the known detectors does not make sense, since it avalanche Avalanche effect for the sensitive detection of Light rays near the intrinsic absorption edge of the used material were designed. This brings with it turns out that the thickness of the pn junction must be chosen so that the pn junction area for incident photons as Waveguide can take effect to be a satisfactory Ratio of quantum efficiency to signal / Get noise ratio.

Furthermore, these avalanche Photodiodes in favor of a not too low cutoff frequency Diffusion lengths for the electron hole pairs on that are in the range of several micrometers. A resolution in the submicrometer range is therefore not possible, since not in the pn junction generated electron-hole pairs to the Diffuse the barrier layer and cause a photocurrent there.

The advantage of a monolithic manufacturing process used according to US 47 58 532 to provide a photodetector, which together with a multiquantumwell heterolaser on one common substrate is provided. By means of suitable Etching is a semiconductor layer system a laser structure and a side-illuminated monitor diode worked out.

The side-lit ones mentioned in the quoted examples Semiconductor photodetectors are therefore not suitable for measurements with high spatial resolution. An increase in Layer doping to determine the layer thickness of the transition  and the diffusion length in the material in the submicrometer range is to bring in these known devices not desirable as this reduces their sensitivity and unsuitable for their original manufacturing purpose would be.

It is therefore an object of the present invention to take a photo detector or a photodetector array with a resolution in the submicron range to provide with which in particular intensity profiles of light rays with a small diameter directly get measured.

This problem is solved by means of a photodetec tors according to claim 1 or a photodetector array according to An Proverb 9

In particular, this happens because the p- and the n- Layer of a semiconductor layer sequence is so heavily doped, that a pn junction occurs, the thickness of which in the local space is in the submicron range. Through the side lighting device of this semiconductor structure parallel to the pn-over A photodetector is created on the surfaces forming the gangway fen, its sensitive surface and thus its Spatial resolution by the thickness of the transition be is true.

One advantage of the photodetector according to the invention is in that it is simple by means of maximization of the detector signal for determining the focus position of a high-resolution microscope lens can be used.  

One embodiment of the invention is the indu layer system that is simplest to manufacture, where the first and second Layer directly on top of each other.

The embodiment of the invention (claim 3) comprises a layer system with a further layer, the arranged between the layers forming the pn junction is. By the appropriate choice of this additional layer can the band structure in the pn transition area of the respective Application can be designed accordingly.

According to the embodiments of the invention (Claims 4 and 5) becomes the pn transition region of such Detector by introducing one too sentence layer between those forming the transition Layers designed so that the sensitive area of the Detector is narrowed further because the intermediate Layer change the band structure in the pn junction area changes that potential walls a diffusion of charge carriers complicate or prevent the pn junction.

According to a further embodiment of the Erfin a photodetector is provided, which also occurs if the object to be measured is not perpendicular Light beam to the pn junction with the required accuracy can work because of its high absorption capacity parasitic generated in the depth of the pn junction Solving power of the detector impairing photocurrents be prevented.

According to another training (An Proverb 7) is the sensitive area of the De tectors using suitable techniques, e.g. B.  lithographic process, to the extent restricted that a high spatially resolving photodetector with a punctiform Detector area arises.

The example in the invention (claim 8) guided semiconductor materials are for such Detector particularly suitable because it is technologically safe be mastered.

According to another example of the invention (claim 9) a photodetector array is provided that consists of a lot number of photos arranged in a matrix detectors. With this arrangement, a spatial Intensity measurement of a light beam with a Resolutions in the submicrometer range possible, the none Scanning the profile with the associated mechanical Difficulties required, but without adjustment problems Real-time measurement allowed.

Possible embodiments of the invention will now be described with reference to the drawing tion explained in more detail.

It shows

FIG. 1A, the layer sequence of a highly spatially resolve the photodetector according to a first embodiment of the invention;

Figure 1B is the corresponding band structure of the first embodiment of the hochortsauf dissolving photodetector.

Fig. 2A, the layer sequence of a highly stationary dissolve the photodetector according to a second embodiment of the invention;

FIG. 2B, the resulting band structure according to the second embodiment of a high local resolution photodetector;

Fig. 3A, the layer sequence of a highly spatially resolve the photodetector according to a third embodiment of the present OF INVENTION dung;

Fig. 3B, the resulting band structure according to the third embodiment of the constricting vorlie invention;

FIG. 4A, the layer sequence of a highly spatially resolve the photodetector according to a fourth embodiment of the present OF INVENTION dung;

FIG. 4B, the resulting band structure according to the fourth embodiment of the constricting vorlie invention;

Fig. 5A, the layer sequence of a highly spatially resolve the photodetector according to a fifth embodiment of the invention;

FIG. 5B, the resulting band structure according to the fifth embodiment of the constricting vorlie invention;

Fig. 6 shows a photodetector structure with the band structure of Fig. 3 of the present invention; and

Fig. 7 is a laterally constricted layer system according to a sixth embodiment of the present invention;

Fig. 8A, the layer sequence of a highly spatially resolve the photodetector according to a seventh embodiment of the present OF INVENTION dung;

FIG. 8B, the resulting band structure according to the seventh embodiment of the present invention.

First, the Schichtfol will now be explained dung gen various embodiments of the present OF INVENTION with reference to FIGS. 1 to 5. In Figs. 1A to 5A, the layer of the respective embodiment and follow shown in FIGS. 1B to 5B, the associated tape structures are Darge provides. Corresponding parts are provided with the same reference numerals in the various embodiments.

In Fig. 1A, a layer 3 of p-doped and a layer 5 of an n-doped semiconductor material A is applied to a substrate 1 . This is well known to those skilled in the art, such. B. possible with various epitaxial processes, diffusion or with ion implantation methods and should not be described here who the. Without limitation, layer 3 could also consist of n-doped system and layer 5 of p-doped semiconductor material. Whether the layer directly adjoining the substrate 1 is p- or n-doped is not essential to the invention.

The choice of the semiconductor material A to be used is from the wavelength to be detected with the associated Absorbance of the semiconductor material dependent. Before  In addition, the absorbency of material A should of the wavelength to be detected should be so large that finding photons after a mean free penetration depth in the Submicron range are almost completely absorbed, otherwise there is a photo hitting the side at an angle can penetrate deeply into the material and become parasitic Generate photocurrents. These parasitic signals are deceptive Photo hitting the sensitive area of the detector and falsify the measurement. At wavelengths Gallium arsenide (GaAs) is shorter than approx. 700 nm Semiconductor material together with Si and Be as a donor or Proven acceptor because it is technologically safe to use is. When choosing the appropriate doping level is next to the resulting layer thickness of the pn junction too the resulting diffusion length of charge carrier pairs to take into account the pn transition area. Both sizes become smaller with increasing doping level and should are in the submicrometer range to achieve the desired resolution to enable

The amount of doping to be chosen, which is in half Conductor material A must introduce to an inventive Obtaining the detector depends on the half used conductor material, from the donors and acceptors used as well as the wavelength to be detected and must therefore be individually adapted to the respective circumstances.

FIG. 1B shows the band structure associated with the layer sequence of FIG. 1A with a valence band 31 and a line band 35 . For better orientation, the Fermi energy 33 is also shown. The pn junction is the area in which conduction and valence bands 35 and 31 are bent. A distance OA, the length of which is typically 500 nm, is plotted on a coordinate axis 20 for the coordinate z perpendicular to the layer sequences. It shows that the thickness or width of the pn junction in the local space is less than 500 nm. The thickness of the pn junction that results when the doping is selected appropriately defines the sensitive region when the layer sequence from FIG. 1A is illuminated vertically. Incident photons are initially only detected in this area and the spatial resolution is thus predetermined.

In Fig. 2A, a further embodiment of the present invention is shown, which differs in its structure from the embodiment of FIG. 1 only in that between the layer 3 of p-doped semiconductor material A and the layer 5 of n-doped A third layer 7 is arranged in semiconductor material A. The third layer 7 consists of the same semiconductor material A as layers 3 and 5 , but is weakly doped or undoped.

The band structure resulting from a layer sequence according to FIG. 2A is shown in FIG. 2B. As can be seen from it in comparison to FIG. 1A, the interim storage of such a weaker or undoped layer 7 initially leads to a slight widening of the layer thickness of the pn junction, which leads to a reduction in the resolution capacity of the detector, but brings technological Advantages with itself. The direct encounter of the heavily doped layers 3 and 5 without an interposed, weakly doped layer 7 means that the probability of non-radiating recombination transitions increases in the pn junction region. The weakly doped or interposed intrinsic layer 7 , however, counteracts this increase in undesired recombination transitions and thus increases the sensitivity of the detector. Thus, depending on whether a higher spatial resolution or a higher sensitivity is desired, a suitable detector can be provided by the suitable choice of the doping of the layer 7 .

The embodiment of Fig. 3A of the present invention includes a layer system that improves the spatial resolution of the photodetector even further. Charge carriers generated outside the pn junction can namely also be “sucked off” through the pn junction within the diffusion length that arises in each case, since the charge carriers can diffuse to the pn junction. The embodiment shown in FIG. 3A differs from the embodiment according to FIG. 1A in that between the layers 3 and 5 of the p- and n-doped semiconductor material A, a third layer 9 is temporarily stored with a second semiconductor material B, the has a larger energy gap or a larger energy gap between the valence and conduction bands than the semiconductor material A. As already discussed above, for technological reasons, gallium arsenide (700 nm and shorter) is particularly suitable for wavelengths to be detected ( GaAs) as semiconductor material A for layers 3 and 5 . Aluminum gallium arsenide (Al _x Ga _1-x As) is preferably used as the semiconductor material B, which has a greater energy band gap compared to Gallium arsenide.

The interposition of the layer 9 between the layers 3 and 5 forms the pn junction between the layers 3 and 5 in the manner shown in FIG. 3B. As can be clearly seen, the pn junction of the semiconductor layer sequence of the semiconductor material A is superimposed on the band structure of the semiconductor material B, E 1 denoting the energy gap between the conduction band of the semiconductor material A and the conduction band of the semiconductor material B and E 2 the energy gap between the valence band of the semiconductor material B to the valence band of the semiconductor material A. The resulting band structure prevents charge carriers generated outside the pn junction that diffuse to the pn junction from contributing to the photocurrent, since these charge carriers are reflected back due to the potential walls E 1 and E 2 . The sensitive area of the detector is thus essentially limited to the width of the pn junction.

By introducing a further layer of a second semiconductor material B, however, it is accepted that the absorption spectrum and thus the sensitivity of the photodetector are shifted towards shorter wavelengths. In the semiconductor material used as an example, gallium arsenide as material for layers 5 and 3 and aluminum gallium arsenide (Al _x Ga _1-x As) as material for layer 9 , this leads to the sensitivity of the photodetector depending on the aluminum content of the Al _x Ga _1-x As layer drops below 700 nm. As a result, the spectrum of light sources that can be used is reduced. This disadvantage is avoided with a photodetector that has a layer sequence according to FIG. 4a of the present invention.

The embodiment according to FIG. 4A of the present invention differs from the embodiment according to FIG. 1A in that a layer system composed of three further layers is arranged between layers 3 and 5 . Seen from the substrate, there is a layer 9 B of a semiconductor material B on the layer 3 which has a larger band gap than the semiconductor material A. On the layer 9 B there is a less doped or intrinsic layer 7 of the semiconductor material A, on which there is in turn a second layer 9 A of the second semiconductor material B with the larger band gap. The conclusion is from layer 5 of the highly n-doped semiconductor material A.

The resulting band structure for the embodiment of FIG. 4A is shown in FIG. 4B. Compared to the band structure shown in FIG. 3B, the band structure shown in FIG. 4B has an absorption capacity in the region of the pn junction which is similar to that of a pn junction which arises when no second semiconductor material B is interposed (cf. Fig. 2B). Thus, a highly spatially resolving photodetector is provided, the resolution of which is essentially limited to the thickness of the layer between the potential walls by the potential walls formed at the edge of the pn junction and whose absorption spectrum corresponds to the embodiment of FIG. 2. The potential walls prevent the diffusion of charge carriers that are generated outside the pn junction in the region of the pn junction. The electrons and holes generated in the area of the pn junction, on the other hand, reach enough energy in the built-in potential of the pn junction so that they overcome the barriers in the form of the potential walls at the edge of the pn junction and can be detected as a photocurrent. It should be pointed out here that the energy gap - the distance between the valence and conduction bands - is a multiple of the size of the potential walls, ie the values of E 1 and E 2 . FIGS. 1B to 5B and 8B are so far "energy" is not to scale.

In Fig. 5A shows a further embodiment of the present invention is described in between the layer 3 of p-doped semiconductor material A and the layer 5 tiertem of n-do semiconductor material A a so-called superlattice (superlattice) 11 is arranged. The superlattice 11 consists of a layer sequence composed of the semiconductor material A and a second semiconductor material B. When using light beams in the wavelength range of 700 nm or shorter, the semiconductor material A can consist, for example, of gallium arsenide. Accordingly, Al _x Ga _1-x As or AlAs is particularly suitable as semiconductor material B, materials A and B being combined into one period from thin layers. The resulting band structure of the superlattice 11 shown in FIG. 5A is shown in FIG. 5B.

Fig. 6 shows in perspective view a photo-detector 40. The detector 40 has a layer system, as it is for. As shown in FIG. 3A, in which a highly p-doped layer 3 , an intrinsically or lightly doped layer 9 and finally a highly n-doped layer 5 follow on a substrate 1 . On the substrate 1 or the highly n-doped layer 9 , two electrical metal contacts 51 are applied, which are connected in a suitable manner to a detection circuit (not shown here). A light beam 50 strikes a surface 57 lying perpendicular to layers 1 , 3 , 9 and 5 .

The surface 57 lies in the measuring plane spanned by the coordinates x and z. The intensity profile of the light beam 50 can, for. B. by a linear displacement of the photodetector 40 or the light beam 50 in the z-direction it can be averaged.

For the photodetector 40 is used as the semiconductor material A Gal lium arsenide (GaAs), which doped with Si results in the n-doped layer 5 , the doping being in the order of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ^-3 . In order to provide the p-doped layer 3 , the gallium arsenide is doped with Be, the doping here being of the order of 1 × 10 ¹⁸ to 1 × 10 ¹⁹ cm ^-3 . The semiconductor material B used consists of Al _x Ga _1-x As, the ratio of aluminum to gallium having x values between 0.1 and 0.35 being set. This results in a detector with a band structure, as is shown schematically in FIG. 3B, E 1 taking approximately the value of 200 meV and E 2 taking approximately the value of 100 meV. The spectral sensitivity of the resulting pn junction is at wavelengths shorter than 700 nm.

For light rays in the infrared range are accordingly z. B. semiconductor materials made of In _x Ga _{1 x} As or In _x Ga _1-x As _y P _1-y with InP or Ge. Compared to GaAs in the red and infrared spectral range (wavelengths longer than 700 nm), these materials have an increased absorption capacity.

FIG. 7 shows an advantageous development of the invention, which differs from the embodiment according to FIG. 6 only in that layers 3 , 9 and 5 are covered in area 57 except for a narrow area by an opaque layer 53 . As a result, the light-sensitive region of the pn junction is laterally narrowed down to a punctiform region 55 as the detector surface.

Fig. 8 shows an array arrangement with a plurality of Li nien photodetectors according to one of the embodiments described above. On a substrate 1 , p-doped layers 3, 3-3, 3-2, 3-1 and n-doped layers 5-3, 5-2, 5-1 and 5 are alternately applied. The layers 3 and 5 are made of the same semiconductor material A and differ only in their doping. Thin layers 9-1, 9-2, 9-3, 9-4, 9-5, 9-6 and 9-7 are between the respective layers 3 and 5 or between the p- and n-doped layers arranged from a semiconductor material B, the energy gap of which is greater than the energy gap of the semiconductor material A. Such a layer sequence gives the band structure shown in FIG. 8B. The intermediate layers 9 produce here respectively in Fig. Potential barriers of height E 1 and E 2, means preventing countries that 9 carriers generated can cause a photoelectric current outside the layers shown 8B. It should be noted that the scale 22 in FIG. 8A does not match the scale 20 in FIG. 8B, the length of the distance OB of the scale 8 A typically being 1 μm. Rather, the band structure shown in FIG. 8B is only a section of the layer sequence shown in FIG. 8A.

The detector array shown in FIG. 8A, like the individual detectors described above, is produced by means of epitaxial methods. The individual layers are contacted separately, so that the photocurrents of the individual line detectors can be measured. The period of the layer sequence 3 - 9 - 5 or the distance between the individual pn junctions is of the order of magnitude of 200 nm. This order of magnitude therefore also indicates the resolving power of the detector array.

Epitaxial processes are particularly suitable for the production of the layer sequences described in FIGS . 1-8, since they are technically safely mastered and allow compliance with the required manufacturing tolerances.

Claims (9)

1. semiconductor photodetector ( 40 ), with:
a first layer ( 5 ) made of an n-doped semiconductor material,
a second layer ( 3 ) made of a p-doped semiconductor material,
the first and second layers being arranged parallel to one another,
electrical contacts ( 51 ) for tapping a photo current,
wherein the first and second layers are oriented such that the direction of incidence of a light beam ( 50 ) to be detected is essentially parallel to the first and second layers, characterized in that
that the strength of the n- and p-doping is chosen depending on the semiconductor materials used so that the resulting thickness of the pn junction in the spatial area and thus the spatial resolution of the photodetector ( 40 ) is in the submicrometer range. 2. Semiconductor photodetector according to claim 1, characterized in that the first layer ( 5 ) and second layer ( 3 ) lie directly on top of each other. 3. Semiconductor photodetector according to claim 1, characterized in that between the first layer ( 5 ) and second layer ( 3 ) a third layer ( 7 , 9 ; 11 ) is arranged. 4. Semiconductor photodetector according to claim 3, characterized in that the third layer ( 9 ) is a semicon terschicht which compared to the first layer ( 5 ) and second layer ( 3 ) a larger energy gap between valence's ( 31 ) - and conduction band ( 35 ). 5. Semiconductor photodetector according to claim 3, characterized in that the third layer ( 11 ) has a multiple fold heterostructure. 6. Semiconductor photodetector according to one of the preceding claims, characterized in that the semiconductor materials used are selected as a function of the light beam to be detected ( 50 ) such that the light beam is almost completely absorbed after a penetration depth in the submicron range. 7. Semiconductor photodetector according to one of the preceding claims, characterized in that the photoemp sensitive pn junction is laterally narrowed by an opaque layer ( 53 ) perpendicular to the direction of incidence of the light beam to be detected, so that a punctiform photosensitive region ( 55 ) is created. 8. Semiconductor photodetector according to one of the preceding claims, characterized in that the semiconductor materials used GaAs, Al _x Ga _1-x As, InP, In _x Ga _1-x As, In _x Ga _1-x As _y P _1-y , Si , Ge are. 9. semiconductor photodetector array with a variety of merged into a one- or two-dimensional array seized photodetectors, characterized by photode tectors according to one of the preceding claims.